The present invention relates generally to apparatus and methods for retorting oil shale and tar sands. More specifically, the present invention relates to an apparatus and method which may be utilized to pyrolyze oil shale and tar sands individually or in varying combinations with a high degree of economy and efficiency.
Since the beginning of modern industrialized society, man's dependence on petroleum for meeting energy demands has increased continually. At the same time, the known resources of petroleum reserves have dwindled. Increased energy demands coupled with dwindling oil reserves has resulted in a massive and concerted effort to develop alternative energy sources. One of the primary alternative sources of energy presently under consideration is oil and combustible gases derived from oil shale and tar sands. Although the present known reserves of oil shale and tar sands are substantial, there has yet to be a commercial implementation of an apparatus and method which can economically and reliably produce usable products from tar sands and oil shale at a competitive price.
Oil shale is a compact sedimentary rock which yields twelve to sixty gallons of oil per ton. The oil-producing substance present in oil shale occurs naturally as kerogen. Kerogen is a complex organic material which may be pyrolyzed at elevated temperatures in the neighborhood of 1000.degree. F. to form shale oil. The requirement that kerogen be heated to high temperatures to recover oil from oil shale has resulted in the use of retorting apparatus to carry out the pyrolysis of kerogen within oil shale. Tar sands, although not containing kerogen, must also be heated to elevated temperatures to recover usable oil products from the tar contained within tar sands. In order to recover oil from tar sands, the temperature must be raised to about 500.degree. F.
Since tar sands and oil shale are many times encountered in the same geologic structure, with major tar sands deposits frequently including "lenses" or layers of oil shale, it is most desirable that a given retort apparatus system be capable of handling both oil shale and tar sands individually and also in combination. A retort apparatus for providing economical and energy efficient retorting of oil shale is disclosed in my prior U.S. Pat. No. 4,146,460 issued on Mar. 27, 1979. Although this apparatus is well-suited for retorting oil shale, the inclined nature of the retort requires that energy be expended when the raw oil shale and tar sands are conveyed upward or elevated to the inlet end of the retort. There is a continuing need for retort designs which are more energy efficient, simple in operation, reliable and economic to use.